The present invention relates to a multielement ultrasonic probe and its production process.
More specifically, the invention relates to a process for the production of an ultrasonic probe comprising a plurality of elementary piezoelectric transducers, juxtaposed either in the form of a linear grating called a strip or in matrix form. The process also relates to the production of a multiannular probe. In this type of probe, the elementary transducers are shaped like rings and are arranged in a concentric manner. These ultrasonic probes are more particularly used in methods for forming medical images by echography.
In such methods, the ultrasonic waves transmitted by the transducers are propagated in the tissues and are reflected on the interfaces (separation or dicontinuity between two media having different acoustic properties). The reflected wave or echo from these interfaces reaches the transducers, which are then used as receivers with a time lag compared with transmission. The time lag increases with increasing distance between the reflecting surface and the probe. This time lag is then measured, and when the time necessary for an outward and return travel of the wave has elapsed, a new pulse can be transmitted.
The echos obtained in this way can be shown, for example, on an oscilloscope screen. A two-dimensional image can be obtained by angularly displacing the transmission beam in the area to be visually displayed, this being called sector scanning.
For ultrasonic imaging by sector scanning, the probes used require small elementary transducers. Thus, it is necessary for the transmission and reception lobe of the ultrasonic waves of these transducers to be circular in order that the sensitivity of each elementary transducer varies only little as a function of the transmission angle. Moreover, the directional characteristic of a transducer is linked with its dimensions and the wider the transducer the more it is directional.
In addition, in order to obtain a correct resolving power, making it possible to distinguish two echo points positioned laterally with respect to the firing line, it is necessary to focus the ultrasonic wave received by the transducers.
In order to permit an effective focusing, the acoustic lens formed, for example, by the linear grating or strip must have a large aperture, i.e. a large size.
The result of these two requirements (sector scanning and focusing of the wave on reception) leads to probes having numerous small components. The small size of the transducer components and their large number cause considerable cabling problems. Thus, the two faces of each elementary transducer must be connected on the one hand to earth and on the other to a connector constituting a connection to the processing electronics. If is very difficult to weld these wires to each elementary transducer and requires a tedious manual operation.